In the conventional gas fired water heater, a gas burner is located beneath the lower head of the tank and waste gases of combustion are discharged from the burner through one or more vertical flues that extend upwardly through the tank. With this type of construction, heat is transferred from the burner through the lower head to heat the water in the tank, and heat is also transferred to the water from the waste gases passing upwardly through the flues.
When the water heater is not in operation, there will be a flow of air by convection through the flues with the resultant transfer of heat from the heated water in the tank to the air passing upwardly through the flues. This can result in considerable heat loss during standby periods. Because of this, the conventional water heater, utilizing internal flues, has an in-service efficiency of less than 70%.
The typical gas-fired water heater has a relatively large diameter flue which is normally connected to a chimney. To prevent blow-out of the pilot light, a burner flame due to downdrafts, the flue is provided with a draft hood. The use of a draft hood can also result in a considerable loss of heat from the building in that heated air from the building can continually flow by convection through the draft hood and the flue to the exterior, with the result that cooler outside air will necessarily be drawn into the building to replace the warm air that is lost through the flue.
Furthermore, there is a tendency in the conventional water heater utilizing internal flues for the water to stratify and be overheated. Heated water will rise to the top of the tank by convection and during periods of short intermittent draws, the heated in the upper end of the tank may be overheated by heat transfer from the hot flue gases passing through the internal flues.
With commerical water heaters, where it is desired to heat the water to sanitizing temperatures of 180.degree. F., it is difficult to heat the water to this temperature without overheating and resultant actuation of the temperature pressure relief valve.
In an attempt to increase the efficiency of the water heater, submersible chamber heaters have been recently developed. With heaters of this type, the burner, instead of being mounted below the lower head, is positioned in a closed combustion chamber located within the lower portion of the tank. Waste gases are forced through or withdrawn from the combustion chamber by a blower and can be discharged directly to the atmosphere.
As submersible chamber heaters of this type do not include internal flues, the standby loss is substantially reduced, thereby increasing service efficiency. Locating the combustion chamber low in the tank also prevents overheating of the water in the upper end of the tank.
Furthermore, as water heaters of this type employ a forced or induced flow through the combustion chamber, the waste gases can be discharged directly to the atmosphere without the need of a chimney.